Granite State Mutual: a full workers' comp pricing & reserving case study
Loss triangles, chain-ladder and Bornhuetter–Ferguson reserving, Mack and ODP-bootstrap risk, a rate indication build-up, a class plan review, and both decisions run through the Actuarium Decision Engine — all fully worked and internally consistent, end to end.
Granite State Mutual is a fictional single-state workers' compensation writer used here as a fully worked, internally consistent case study. The book spans accident years 2017–2024, growing from 548M of covered payroll. We have cumulative paid and reported (incurred) loss triangles evaluated at 12-month intervals from 12 to 96 months of maturity (in $000s), a matching reported claim-count triangle, on-level history from 8 rate revisions, and a five-class-code detail (8810 clerical, 5645 carpentry, 8380 auto repair, 7380 drivers, 9079 restaurant) for the class-plan review.
WC development is long-tailed on the indemnity side (permanent-partial and permanent-total claims can stay open for decades) but the reported triangle firms up faster than paid because case reserves are set close to full value soon after a claim is diagnosed, while payment is a slow drip. That paid/reported dynamic is deliberately built into the synthetic factors below: reported development from first report (12mo) to ultimate is roughly , versus for paid.